RFLP (restriction fragment length polymorphism) analysis has proven highly successful in mapping and discovering new genes in eukaryotic organisms. RFLP marker probes consist of polynucleotide sequences that specifically hybridize to a region of the chromosome. These chromosomal regions of hybridization are revealed to be polymorphic between individuals of the same species when the chromosomal DNA is digested by restriction endonucleases and analyzed by hybridization analysis. Different RFLP alleles are distinguished from one another on the basis of the hybridization banding patterns produced after size separation. Genetic linkage analysis between RFLP markers and uncharacterized genes has proven to be a useful technique for isolating and mapping uncharacterized genes of interest. Although the RFLP marker has most frequently been used to identify the chromosomal disruptions responsible for genetic diseases, it is also of interest to use RFLP markers in deciphering other complex genetic regulatory questions, such as sexual development in animals.
While the genetics and biochemistry of sex determination in mammals has been the subject of extensive scientific investigation, similar studies have not been carried out with respect to birds. This is surprising in view of the commercial importance of numerous avian species e.g., chickens and turkeys. It is of interest to provide research tools useful for deciphering the complex process of genetic sex determination in birds. Sex-specific genetic markers are of particular interest. Such markers may be used to sexually identify immature birds prior to the development of gender specific morphological differences. Early sexual identification is an important consideration when breeding those birds that become sexually mature prior to the development of external sexual characteristics. Accordingly, there is interest in providing methods for preventing undesired matings by permitting gender identification (and gender separation) prior to the development of sexual maturity.
Genetic sexual identification is also useful in the breeding of rare bird species with unidentified secondary sexual characteristics; captive breeding programs may thus be effectively organized.
Sex chromosomes, as opposed to autosomal chromosomes, differ with respect to one another in size and genetic composition. Thus, some regions of one sex chromosome contains genes which have no corresponding allele on the other sex chromosome.
One of the principal ways in which the sex chromosomes of birds differ from man and other mammals is that the female bird is the "heterogametic" sex, having Z and W sex chromosomes. In mammals, the male is the "heterogametic" sex having both X and Y chromosomes whereas the female is "homogametic" having two X chromosomes.
It is of interest to provide RFLP genetic markers suitable for the identification of DNA regions which are diagnostic of the sex of the bird, where the DNA regions may be common to the Z and W chromosomes such that RFLP's unique to each sex chromosomes may be detected; or the DNA region is unique to one of the sex chromosomes, so that the amount or presence of the RFLP will determine the sex of the bird. Such genetic markers permit the identification of the chromosomally specified sex of an individual bird based on analysis of a DNA preparation derived from the bird.
Relevant Literature
Halverson J., Dvorak, J., Flammer, K. 1985. A new method of avian sex determination- identification of the W body by C-banding of erythrocytes. Proceedings of the Annual Meeting of the Association of Avian Veterinarians. 1985. Boulder, Colo.
Halverson, J., Rauen, K., 1988. The molecular approach to poultry breeding. Proceedings of the Thirty-seventh Western Poultry Disease Conference and Molecular Biology Workshop. 1988. Davis, Calif.